Field processing equipment for oil wells mounted at a subsea location



B. s. BURRUS 3,545,215 FIELD PROCESSING EQUIPMENT FOR OIL WELLS MOUNTED AT A SUBSEA LOCATION Dec; 8, 1970 Filed Dec. 5, 1968 s Sheets-Shet 1 INVENTOR, BIL L s. I BURRUS TO STORAGE 4- AND DISPOSAL z ATTORNEY as. BU RUS ,2

FIELD PROCESSING EQUIPMENT FOR OIL"WELLS 4 MOUNTED AT A SUBSEA LOCATION A Dec. 8,1970

Filed Dec. 5, 1968 3 Shets-Sheet 2 INVENTOR. HILL 5. BURRUS ATTORNEY Dec. 8, 1970 B. s. BURRUS FIELD PROCESSING EQUIPMENT FOR OIL WELLS MOUNTED AT A SUBSEAIOCATION 3 sheets sheet 5 Filed Dec; 5, 1968 I I l I llufl l.|.||||lllllllll|lllll%ullllll [mm 1 km @w I mm H M N 7 l IELLZHHFH I Q JAM. J m hf m. w mm w wm .UWI I I N \F. .2 av ww km ow QM NV INVENTOR. BILL 5. BURRUS ATTORNEY United States Patent 3,545,215 FIELD PROCESSING EQUIPMENT FOR OIL WELLS MOUNTED AT A SUBSEA LOCATION Bill S. Burrus, Tulsa, Okla., assignor to Combustion Engineering, Inc., New York, N.Y., a corporation of Delaware Filed Dec. 5, 1968, Ser. No. 781,541 Int. Cl. B63c 11/00 US. Cl. 61-69 6 Claims ABSTRACT OF THE DISCLOSURE Portions of subsea equipment are covered by inverted bell-like structure and filled with gas to provide a dry environment for the equipment. A source of environmental gas at the subsea location is indicated and means for purging and replacing fluids within the bell-like struc ture is disclosed.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to providing a gaseous environment for selected portions of subsea equipment. More particularly, the invention relates to providing gasfilled enclosures about subsea equipment, which enclosures can be purged with non-toxic gas, and access for service personnel and life support gases for breathing by the personnel.

Description of the prior art As the oil industry has rushed into the sea to reap the harvest of oil discovered beneath the sea bottom, the operating problems have rapidly subdivided. The discovery of oil beneath the sea, drilling under water, producing from subsea wellheads, processing the fluids at the wellheads and transporting the products to shore are only some of the subdivisions of the problems. In areas of relatively shallow water depths, platforms have been built up from the bottom and the techniques developed on shore have been merely transferred to the platforms having this damp underfooting. At present, oil fields are being planned for production which lie 15010 1,000 feet beneath the surface of the distinctly hostile environment of the sea.

The casual observer concludes it is common practice for a simple run of pipe to be connected to the wellhead to transport oil well fluids to shore. In many instances, where it is but a short distance to shore, this is the present practice. However, the two-phase flow of gas and oil induces a large pressure drop in a flow line, rapidly limiting the practical distance over which the blood, guts, feathers and all produced by a well can be conducted. Also, the cooling of the unseparated phases by the sea, as a heat sink, can form hydrates from the fluids. This solid material induces additional pressure drop in a flow line. With newly drilled wells located many miles from shore their produced fluids must be separated in the so-called field processing near the wellhead.

The equipment to separate oil well fluids includes relatively large vessels with simple controls to regulate pressure and fluid levels within the vessels. A stable base must be provided for this equipment. Obviously, there is a huge range of problems oin providing the bases at wellheads in 150 feet or more of water. Still another range of problems arises in controlling the flows into, and out of, the vessels, along with the pressure and levels within the vessels.

In summary, the discovery and drilling of wells at more than 150 foot depths has run far ahead of the de- "ice velopment of processing and transporting. The relatively simple processing by separation and dehydration has yet to be carried out successfully beneath the surface of the sea. All the forces within the industry clamor for solution of these problems on wells which are located at depths of feet and more.

This invention first assumes the basic problem of support of the separation equipment has been solved. A stable base has been provided for the equipment. The invention here focuses upon the specific problem of providing a gaseous environment for certain portions of the separation equipment. There may be other arrangements for removing the equipment to the surface for service, repairs and replacement. However, in situ, the equipment is vulnerable to marine growth and providing a gaseous environment for selected portions of the equipment will militate against marine accumulations interfering with the normal function of the equipment.

Additionally, there is the problem of personnel access to the gas-protected equipment. The gas available at the subsea location may be both internally and externally toxic. Usually some form of natural gas is contemplated, but the composition of this fluid may vary widely.

SUMMARY OF THE INVENTION A principal object of the present invention is to provide a gaseous enviornment about portions'of subsea equipment with gas from a subsea source.

Another object is to purge environmental gas of a toxic nature from about the equipment with a fluid which is non-toxic to service personnel.

Another object is to provide access for service personnel to the equipment.

The invention contemplates a form of bell-like structure inverted over and around selected portions of subsea equipment andsupplied gas available at a subsea location about the equipment to obviate marine growth upon the equipment and provide a satisfactory operable environment for controls included in the equipment. Further, the invention contemplates a purge system which will replace any toxic subsea gas with a non-toxic fluid to enable service personnel to work on the equipment, with means to re-establish the former atmosphere when personnel depart from the work locale. Finally, it is contemplated that a personnel transfer lock will be provided to provide access for service personnel into the bell for specific access to the equipment.

Other objects, features and advantages of the invention will be apparent from the following detailed description and claims, with references to the accompanying drawings in which:

FIG. 1 is an isometric view of a subsea producing oil property in which a platform with oil field process equipment and protective housing embodying the invention is in place and operational;

FIG. 2 is a plan view of the: platform showing the piping and control system for the process equipment which is encapsulated by the protective bell-shaped structure;

FIG. 3 is a side elevation of the platform, equipment and hell with a section of the entry lock; and

FIG. 4 is a front elevation of the platform, equipment and bell with a section of the entry lock.

DESCRIPTION OF THE PREFERRED EMBODIMENT-GENERAL FIG. 1 discloses the complete submerged production processing facility receiving the raw production of at least oil wells 1 and 2 which are completed on the marine bottom. The production is removed from the submerged facility by conduit 3. The terminal equipment for conduit 3 is not indicated for it is not pertinent to the present invention.

The facility includes at least three basic components. Anchor is on the marine bottom 6. Buoyant support structure 7 is tethered above anchor 5. Pontoon structure 8 is locked to the support structure. The production equipment is mounted on deck 9 of pontoon 8 from where it serves the oil wells 1, 2 and delivers to storage and disposal equipment the petroleum fluids of the wells.

The surface of the body of water in which the facility is submerged is indicated at 10. A surface craft 11 is shown, plying the waters in normal commercial trade, the tethered buoyant support and pontoon structure being Well below such activity near the surface 10.

The wells are connected to the pontoon equipment by flow lines 12. These lines 12 are high pressure conduits which should be given stable support to obviate their failure. Therefore, the lines 12 are shown rising to the upper surface of support structure 7 where they are anchored securely and joined at 13 to the input conduits of the pontoon equipment. The specific anchoring structure is not disclosed for it is not pertinent to the present invention.

The arrangement with which to anchor and support conduit 3 is similar to that for lines 12. The conduits simply lead from their junction at 13 with the output lines from the production equipment. They are led over the side of the support structure 7.

Support structure 7 and pontoon structure 8 are locked together at positions 15. Again, details of the locking structure are not disclosed. When the structures are unlocked, pontoon 8 is allowed to rise to the surface as required to repair, Service or replace parts of the production equipment mounted on the pontoon deck 9.

The lines tethering the support and pontoon structures 7, 8 to anchor 5 are indicated at 16. These lines are fixed by one end to support structure 7 with fixtures 17. With these lines the support and pontoon structures are winched down to the location shown. Pontoon structure 8, once it is unlocked from support structure 7, can be winched between the surface and the location shown by taking up, and letting out, lines 18. The production equipment can, thereby, be brought to the surface for repair, service and replacement. However, it is contemplated that the depth of the equipment from the surface would be small enough to enable diving technicians to reach and service the equipment in situ.

The winches for lines 18 are indicated at 19 as mounted on the edge of the pontoon structure 8. In general, the winches are mounted on a foundation which extends beyond the rim of pontoon 8 to contact support structure 7 and maintain their basic concentricity. The locks then secure these structures against vertical displacement,

relative to each other.

At this point of generalization, it is emphasized that although the three basic components are each illustrated in the specific form of a torus, this is not necessary to their functions. The term torus is used in its broadest sense. Actually these bodies may be formed of multiple straight sections which are only generally classified as toroidal in the completed form. The form of the torus was found to have several advantages for this construction, but the practicalities of construction could dictate some modification.

In any event, the broad concept of three buoyant structures arranged as shown in FIG. 1 is developed clearly. The anchor is adjustable in buoyancy so it may be sunk to the marine bottom as shown. The support structure is tethered to the anchor a predetermined distance below the surface. The equipment-bearing pontoon is drawn down to, and locked on, the support structure. The final combination supports oil well production equipment at an eccessible depth, with satisfactory stability and at a cost far below that of a tower s rtwt l suppo d from the marine bottom.

4 CONNECTIONS TO PROCESS EQUIPMENT In FIG. 1 the connection locations 13 indicate where the flow line risers from the wells join the input lines to the process equipment and where the output and flare lines join riser lines leading from the equipment. These connections are depicted here as flange structures mounted on the riser support structure 7.

The ends of the conduit system on deck 9 are mounted with great stability on platform-type bases attached to the upper surface of support structure 7. Conduits 12, 3 and 29 leading to deck 9, and those leading from deck 9, have flanges on each end which are vertically oriented. The flanges mate to connect these several risers to the lines on deck 9, thus forming the connector structures referred to in general by numeral 13. The specific construction of these flanges for subsea service is not disclosed. Obviously every detail of this nature must be carefully considered for the demands of subsea environment.

Each input and discharge conduit is formed with a long, unsupported bend for at least the reason that some movement is thereby provided for mating flanges to accommodate minor misalignment, as well as movements of the buoyant structures 7 and 8 relative to the ocean floor.

A more detailed disclosure of the process equipment support and anchor structures, the connectors 13, the locks 15, the winch and guides 19, and other elements shown in the diagram of FIG. 1 is made in US. patent application S.N. 773,121, filed Nov. 4, 1968.

PROCESS EQUIPMENT FIGS. 2, 3 and 4 disclose the process equipment mounted on pontoon 8 as an oil and gas separator and nonemulsified water removal structure (or so-called free water knockout) combined in vessel 20, and a test separator for individual well testing shown in vessel 21.

It must be understood that this equipment shown in the drawings is merely representative of oil field process equipment. It is theoretically possible to have every form of this type equipment, including field storage tanks, mounted on the pontoon deck 9. It is also likely that certain equipment would be mounted on the marine bottom, certain other on the pontoon, other on the water surface, and yet other at a shore location. It is essential that the concept of a controlled environment within inverted bell or capsule 22 not be limited by the showing of only the simple stage separation equipment shown in these drawings, as they are purposely simple representatives of the large category of field process equipment. The choice of process vessels is not material of itself to the inventive concept.

THE CAPSULE The capsule 22 houses the valving, metering, and con trol components of the process equipment 20, 21. Capsule deck 23 supports the control panel 24, various line supports and tie-downs, and the divers during occupancy. A second deck 25 supports in part the air lock structure 26 and the under deck water discharge line 27. The various views of the capsule in FIGS. 1 through 4 illustrate one representation of these components within the capsule. While it is possible that in more sophisticated installations all of the process equipment and controls would be encapsulated, in the embodiment of this description all of the equipment is not enclosed.

The shells of these vessels 20 and 21 can be protected from the sea by any of several well-known coatings or paints. To focus attention on the primary function of the capsule in its job of protection of the brain of the process, viz. the controls, only such controls are shown protected within the capsule structure. The external shell of such vessels seldom requires more than visual inspection, but should maintenance be required, the pontoon 8 of the platform can be raised to the surface.

THE CAPSULE ENVIRONMENT It would be diflicult to devise a more trying circumstance for either human activity or operation of equipment than that extant subsurface of the oceans. The water is, of course, uninhabitable by man without an artificial breathing atmosphere; it requires of him a high degree not only of psychological acclimatization, but also new skills of perception, concentration, and dexterity in its high pressure, nearly weightless, and dark surroundings. Likewise, both the chemical constituents and the inhabitants of the waters are constant threats to machine and man. The microscopic barnacle for instance quite literally consumes the metals it attaches to. No wonder then that man has invaded the void of space before exploiting the wealth of the oceans.

Furthermore, subsea oil field process becomes increasingly difficult as its art evolves to a continuously more advanced state. For example, many recent techniques use increased process temperatures and fine heat balance, while the waters provide an infinite heat sink and an admirably efiicient heat exchanger.

These factors, together with all the usual problems inherent in treating the corrosive, toxic, combustible, three-phase hydrocarbon reservoir fluids, point out the necessity for subsea environmental control and suggest the difficulty and broad range of problems to be met.

The invention provides a solution to many of these problems. FIG. 2 shows a possible arrangement of the controls necessary to operate separators and 21. The gas line 28 exits separator 20 and is run to flare through conduit 29. The oil line 30 from the separator is metered and valved within capsule 22 and the oil is transferred to further process or storage through line 3. Water removed from the well streams is discharged through line 27 into the sea. Back pressure valves 31, 32 control the water and gas discharge from the separator vessel, and valve 33, the operating pressure within the bell structure 22. The well streams enter the process through lines 12, manifold 34, and line 35. FIG. 2 suggests an areal arrangement, and FIGS. 3 and 4 a spatial arrangement of these parts.

i The capsule will normally contain a gas atmosphere composed of produced hydrocarbon gases generated out of the incoming reservoir fluids by separator 20. Constantbleed valve 33, shown clearly in FIG. 2, can be set to regulate the amount of gas bleeding into the capsule 22. The bleed rate will be set for the particular depth of submergence to provide that the minimum amount of gas will escape from the capsule into the sea. A regulating valve could be used alternatively or in conjunction with a bleed-type valve 33. Gas pressure available from separator 20 is presumed to be high enough in normal situations to overcome the hydrostatic head.

The hydrocarbon gas atmosphere within the capsule provides a sure means for protecting the equipment from the pernicious and degenerative action of the sea and sea life. It also prevents the oxidation which would be experienced by exposure to a normal surface atmosphere.

In this reduction to practice, the source for the desired gas is reservoir gas, and the pressure within capsule 22 can easily and economically be held at ambient.

Should it be necessary to purge the gas atmosphere from capsule 22, valve 36 or 37 would be opened and valve 33 closed. Evacuation of the gas would permit the sea water to fill the space beneath the capsule. Substitution of a water environment beneath the capsule for the gas might be desirable for numerous reasons. for example, 1) to purify the hydrocarbon gas atmosphere should it become contaminated by the divers oxygen exhaust, and thus potentially explosive, during their presence in the capsule, or (2) should the divers prefer to work in the near weightlessness of a water atmosphere rather than a gas atmosphere.

The hydrocarbon gas atmosphere would be re-established by closing valves 36 and 37 and opening valve 33. A diver could open a valve directly connected to the pressure in gas line 28, such as shown at 38, to quickly blow the water, then close that valve and open constantbleed valve 33, as valve 33 would in reality be set at a low bleed rate to hold bell 22 pressure only slightly in excess of hydrostatic, for example, within a fraction of 1 oz., to avoid wastage of, as well as contamination of the sea with, the natural gas.

The gas atmosphere re-established could alternatively be a breathable gas prepared for life support. A supply of this gas under sufficient pressure could be connected to the capsule to blow the water from the capsule. For ex ample, pressure vessel 41 could contain the proper life support gas for breathing by service personnel at work in the bell; a gas umbilical line 42 could also be extended to the surface to supply adequate amounts of breathable gas of proper composition and pressure to diverse within the bell. Also, the hydrocarbon gas could be directly purged with the breathable gas.

ACCESS An open or Wet bottom is contemplated for the preferred embodiment, and would thus provide only partial encapsulation of the controls in the sense that they would not be totally enclosed by a man-made structure.

Entry lock 26 is provided for diver entry to the capsule. The water/ gas interface within the bell and below deck 23 is indicated by numeral 39. This quick-entry and escape feature of the partial enclosure is a chief reason for its use in the preferred embodiment. Though a sealed and pressurized totally enclosed structure offers a shirtsleeve work environment, emergency exits become impossible.

The grating which forms dock 430 is designed to receive a personal transfer unit. When it. is impractical for the divers to swim to the equipment location, it is contem plated that they will be lowered in a bell-type diving structure with a breathable atmosphere. This method will provide conservation of diver energy and self-contained air to allow longer working times in the capsule, safety from sea animals, and so forth.

SUMMARY It is seen that the enclosure system disclosed, covering the process controls and containing a gas atmosphere of natural gas from the producing reservoir, will solve the several problems herein delineated. When compared to alternative systems, the system is also seen to provide an optimum of personnel safety, mobility, and psychological security, a minimum shipping and handling weight and size, and a reasonable investment cost.

It is stressed that the process equipment depicted is only a basic example of the wide range of equipment which will be employed with this invention.

It is also stressed that the environmental control gas need not be a natural hydrocarbon gas. It may be a gas of any composition from any source, so long as the source is local to the equipment, such as from the petroleum reservoir described, from storage tanks or other process equipment local to the subsea support structure, from a vessel on or near the platform, or from an umbilical line to the surface.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the method and apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A module of equipment designed and arranged to carry out a work function at a subsea location, including:

a support :for the module at the subsea location,

a bell structure held in an inverted attitude over a predetermined portion of the module so as to maintain a gaseous fluid captured beneath the bell about the predetermined position of the module,

a supply of gaseous fluid available at or near the subsea location which is connected to the bell so as to maintain gaseous fluid captured beneath the bell,

and means for purging the bell of the first gaseous fluid with a second predetermined fluid.

2. The module of claim 1, including means for personnel to gain access to the interior of the bell for working on that portion of the equipment protected by the gas trapped by the bell.

3. A system for protection and service of subsea equipment at a subsea location, including:

a subsea support for equipment,

a module of equipment mounted on the support to carry out a work function,

a bell structure mounted about a selected portion of the equipment,

a first source of gaseous fluid at the subsea location connected to fill the bell structure and maintain the equipment within the bell surrounded with the gaseous fluid and thereby militate against the accumulation of marine growth on the equipment,

a second source of fluid which is non-toxic to personnel,

and a system for connecting the bell structure to the second source so as to purge the hell with the nontoxic fluid prior to entry of service personnel.

4. The system of claim 3 wherein the second source of fluid is gas capable of life support.

5. The system of claim 3 wherein the first source of gaseous fluid is the hydrocarbon gas of an oil well at the subsea location.

6. The system of claim 3 including, a lock structure connected to the bell with which personnel can gain access to the interior of the bell.

References Cited UNITED STATES PATENTS J. KARL BELL, Primary Examiner US. Cl. X.R. 6l46.5; 114.5 

